1. Field of the Invention
The present invention relates to a wafer probing test machine for testing each of the pads on a semiconductor wafer chip and more particularly, relates to an improvement of the wafer transfer system for transferring the wafer between a cassette stage and a test stage.
2. Description of the Related Art
In the course of testing wafers of semiconductor devices, pads of the wafer chip are contacted with probes to test or examine whether or not the electric circuit on each chip is disconnected and also to test electric characteristics of each chip. The wafer probing test machine (or wafer prober) is used for this wafer test.
The wafer prober includes a test section and loading/unloading section. The test section includes a test stage and a probe card. A plurality of probes are planted on the probe card and each of the probes is electrically connected to a tester.
The wafers are carried one by one from the loading/unloading section into the test section and the pads on each semiconductor wafer chip are contacted with the probes. A signal is applied from the tester to the electric terminals to check whether or not the electrical circuit on the chip is disconnected.
In the case of the conventional wafer probers, the place where the wafers are taken out from and returned into the cassette is located on the body frame of the prober because this outside place makes it easy to handle wafers and cassettes. According to this conventional wafer prober, the wafer cassette is mounted on an elevator at the loading/unloading section. While intermittently lifting the elevator at a certain pitch, the wafer is picked up by a pincette (or vacuum holding) system. The wafer thus took out is then carried into the test section defined by the body frame.
As the circuit on each of the semiconductor devices is integrated more and more, it is necessary that the atmosphere around the wafers be made cleaner because the existence of particles adhering to any of the wafers make them faulty. It has been therefore been attempted that the atmosphere in the clean room be kept as clean as possible and that particles caused by the machine itself be kept as few as possible.
In the case of the conventional wafer probers, however, the wafer take-out/return place is located outside of the machine, that is, on the body frame of the machine. This makes it difficult to prevent particles also caused by operators' behaviors around the wafers from adhering to the wafers.
On the other hand, the cleanliness in the clean room can be made extremely high by improving the flow of atmosphere in the clean room and enhancing the capacity of filters used. However, the clean room thus built so high in its construction and maintenance costs as to make it impractical or not economical.